Electric motor circuit breaker or protector



June 30, 1959 A. DIEBOLD 7 2,892,910

ELECTRIC MOTOR CIRCUIT BREAKER OR PROTECTOR Filed March 1, 1955 INVENTOR. Anton Diebold ATTORNEYS United States Patent U i ELECTRIC MOTOR CIRCUI'I BREAIGIR OR PROTECTOR Anton Diebold, New York, N.Y., assignor to The Wilcolator Company, Elizabeth, N.J., a corporation of Delaware Application March 1,1955, Serial No. 491,333

9 Claims. (Cl. 200113) My invention relates to improvements in circuit breakers for protecting electric motors against current overloads and more particularly to a circuit breaker of the type including a snap-acting bimetallic thermostatic blade adapted to open an electric motor circuit in response to the occurrence of a current overload or heating.

Circuit breakers of the general type covered by the invention are now manufactured and in use in which a blade is arranged to open a motor circuit. These devices, however, are relatively expensive to manufacture and difiicult to calibrate because the blade is carried by and mounted in a housing on a small threaded bolt which is used for calibrating purposes. These parts are not only relatively expensive 'to make and assemble but are difficult to handle and use in calibrating the circuit breaker. Furthermore, if one of these devices is found, after test, to be inaccurate, it is extremely difiicult to recalibrate the blade.

The primary object, therefore, of the present invention is to provide a snap-acting 'bimetallic'blade-type circuit breaker which is relatively inexpensive to manufacture and which requires no special tools for calibration.

A further object of the invention is to provide a thermostatic bimetallic blade circuit breaker which is easily calibrated to predetermined response temperatures for opening and closing the circuit protected thereby.

A further object of the invention is to provide a circuit breaker of the type under consideration, in which the blades are readily exchangeable or replaceable.

Another object of the invention is toprovide a circuit breaker in which the bimetallic blade is readily adjustable and resettable, but which is rigidly held to the blade mounting or housing for normal operation.

In accordance with the present invention, the improved circuit breaker comprises a construction including a mounting unit provided with a pair of terminal connections and a bimetal snap-acting blade unit secured to the mounting and normally connecting the terminals of the mounting unit, and a friction-grip or press-fit means including elements respectively carried by the mounting unit and the blade unit for securing and holding said units together in a rigid readily adjustable operative relationship.

In a preferred construction, the friction-grip or pressfit means comprises a stud having knurling on its periphery and fixed to one of the units and fitting snugly in a bore in the other unit. The stud is preferably fixed to the bimetal blade at approximately its center and extends generally at right angles thereto for convenience in handling and assembly, while the mounting or housing is provided with a bore into which the stud carrying the bimetal blade is pressed to the required extent. The stud fits snugly in the bore so that the blade unit is rigidly supported with respect to the mounting or housing.

Calibration of the improved circuit breaker is readily accomplished by pressing the stud into the bore to the required extent while the entire assembly is maintained at the required calibrating temperature.

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The improved circuit breaker construction includes other features and advantages which are described more in detail hereinafter in connection with the accompanying drawings showing an embodiment of the circuit breaker.

In the drawings:

Fig. 1 is a plan view of a bimetal blade circuit breaker constructed in accordance with the present invention;

Fig. 2 is a vertical sectional view of the circuit breaker shown in Fig. 1, taken on the line 2-2 with the circuit breaker switch in closed position;

Fig. 3 is a horizontal sectional view taken on the line 3-3 of Fig. 2; and

Fig. 4 is a broken vertical sectional view similar to that of Fig. 2, showing the switch of the circuit breaker in open position.

Referring to the drawings, the improved circuit breaker shown therein comprises a mounting or housing 10, for example, of molded Bakelite having a bottom 1'2 through which an electrical terminal 14 extends. The terminal 14 includes a bent-over portion 16 in the housing to provide a contact surface which may have a top of silver inlay. One end of a heater wire 2% is Welded to the contact portion 16, as shown in Fig. 2, while its other end is welded to a similar terminal 22, shown in Fig. 3, which extends through and projects from the bottom 12 of the housing.

The housing unit or assembly includes a tubular rivet or insert 24 extending centrally through the bottom wail 12 with its upper portion resting on a lock washer 26. The rivet also extends through a hole in a terminal 28 recessed in the bottom 12 and including a downwardlyextending portion 30. The tubular rivet 24 is riveted against the lower surface of the terminal 28. The lock washer 26 is a standard shake-proof lock washer, as shown in Pig. 3, with external serrations in alternating opposed directions and the terminal 28 may be provided with locking tabs spaced apart and which extend into the Bakelite bottom 12. The lock washer 26, together with the terminal 28, prevents any turning of the insert or tubular rivet 24 so that it is held rigidly in the housing.

The bimetal blade unit assembly comprises a bimetal blade 32 of bimetallic sheet material having the general circular outline shown in Fig. 1. This blade includes an outer body portion 34 having a spherically-shaped formation, as shown in Fig. 2, and includes a tongue 36 integral with the body 34 and spaced therefrom by a U- shaped slot 38. The tongue 36 is substantially symmetrically arranged with respect to the body of the blade and supports the blade on a stud 40. As shown in Fig. 2, the stud 40 includes an enlarged shouldered portion 42 on which the tongue 36 rests and an elongated downwardly-extending portion provided with knurling 44 and a tapered end 46. The stud 40 also includes an upper portion extending through a hole in the tongue 36 and a hole in a stop 48, the top portion of the stud being spread and riveted over at 50 to non-rotatably secure the stud to the blade 32 and the stop 48. The blade unit includes a contact 52 welded to the undersurface of the body of the blade directly opposite the projecting'or free end of the tongue 36. p

The knurling 44 on the stem of the stud 40 is shown in the form of serrations or striations. When the blade unit is assembled with the housing unit, the blade unit is oriented so that the contact 52 engages the contact 16 and the knurled stud is pressed into the bore of the rivet 24. These elements are made so that the stud fits snugly and rigidly in the bore of the rivet so that the blade will be firmly retained in any position to whichthe stud is pressed into the rivet. The rivet 24 may be made of some relatively soft metal, such as brass, and the stud 40 made of some harder metal, such as steel, so that the knurling on the stud may cut slightly into the inner peripheral surface of the bore in the rivet. However, a press fit between a stud and a rivet bore with smooth surfaces will hold the blade and housing units against relative movement either rotationally or longitudinally. The end taper 46 of the stud 40 facilitates assembly, since it aids in initially centering and starting the stud into the bore of the rivet 24.

The bimetal blade 32 is made from bimetallic material with its low-expanding side on top and its highexpanding side on the bottom. The blade is subjected to a preforming operation, so that it is provided with a symmetrically-shaped spherical deformation, as shown in Fig. 2. When the blade is heated, its high-expanding side causes the blade to substantially reverse its shape, which occurs with a snap action to lift the contact 52 away from the contact 16. During the heating of the blade, the tongue bends upwardly with respect to the stud 40 opposite the contact 52 and thereby increases the contact pressure up to the point when the contact 52 is snapped away from the contact 16. In this latter position, the blade has in general the shape shown in Fig. 4 of the drawings.

When the blade and housing units are assembled, the stud is pressed-in only until the contact 52 engages the lower contact 16. The blade is then ready for calibration to be adjusted to a predetermined operating temperature according to the use to which the circuit breaker is to be put. The calibration is effected by soaking the circuit breaker in an ambient temperature which is the same as the operating temperature to which the blade is to be calibrated. Assuming, for example, that the blade is to have a natural operating temperature of about 30 F. above the calibrating temperature, the stud is slowly pressed deeper into the housing, while at the ambient temperature, until the blade snaps open. The circuit breaker will then have an operating temperature equal to the ambient temperature in which it was calibrated.

If it is desired to increase the operating temperature of the circuit breaker, it is merely necessary to push back the end of the stud slightly and recalibrate the circuit breaker in the manner described above.

For practical reasons, the bimetal blade of the circuit breakers of this type are always made to reset at a temperature slightly below the mean required resetting tem- .perature. During production, calibrationand testing of the circuit breakers, some of them may operate to reset below the minimum temperature requirement. Such circuit breakers can be adjusted and the reset temperature raised by use of the stop 48 which extends out over the body of the blade at the position of the contact 52. The stop 48 is made of metal and its free end may be bent up or down, as indicated in Fig. 4. In order to raise the reset temperature of the circuit breaker, the free end of the stop 48 is adjusted downwardly to restrict the opening movement of the blade. This adjusted stop prevents the blade from opening up fully to its natural opening position and, consequently, causes a quicker blade resetting, which is synonomous with a higher temperature resetting.

The circuit breaker may or may not include the heater wire 20, but it is usually provided in motor circuit breakers where a quicker response of the circuit breaker is required. The heater wire is relatively heavy stiff resistance wire and is rigidly held in position in the housing by the two terminals 14 and 22, which are, in practice, rigidly staked to the housing. The heater 20 is arranged in series with the circuit through the bimetal blade unit, the circuit breaker being adapted to plug into a motor or its operating circuit so that the terminals 22 and 30 bridge one of the motor circuit leads from the current supply. When the heater is used with the blade, the terminal 22 is not used, or is used for some other connection not affecting the circuit breaker, ,If the heater .4 20 is not to be used, the terminals 14 and 30 are connected in one of the motor circuit leads and the terminal 22 is not used.

If the current to the motor becomes excessive, the bimetal blade is overheated and snaps to open position, thereby interrupting the circuit. This will occur without the heater 20. With the heater 20 in the unit, however, the blade 32 is heated by the heater 20 as well by the current flow therethrough so that the circuit breaker opens much more quickly.

The improved circuit breaker construction of the present invention provides a circuit breaker which is relatively inexpensive to manufacture and one which is easy to calibrate for both operating and resetting tempera tures. Furthermore, if it is found that a particular circuit breaker does not test out or operate properly, the blade unit can readily be replaced by a new one within a matter of seconds without in any way altering the housing assembly. Neither the calibration of the circuit breaker nor the replacement of the blade unit in any way affects the position of the heater nor its relationship to the bimetal blade. The elements of the circuit breaker are easily and readily constructed and assembled, calibrated and adjusted, and a rigid construction is provided which is not affected by repeated operation of the bimetal blade.

I claim:

1. A circuit breaker comprising a mounting unit provided with a pair of terminal connections, a bimetal blade unit secured to the mounting unit and normally electrically connecting the pair of terminals of the mounting unit, and a press-fit means including elements carried by and independently fixed to each of the mounting unit and the bimetal blade unit respectively for securing and holding the units together in a rigid infinitely adjustable operative relationship.

2. A circuit breaker as claimed in claim 1, in which the press-fit means comprises a stud fixed to one of said units fitting snugly in a bore in a part fixed in the other unit.

3. A circuit breaker as claimed in claim 2, in which the stud is provided with knurling on its periphery for frictionally engaging the inner periphery of the bore in the part fixed in the other unit.

4. A circuit breaker as claimed in claim 3, in which the knurling on the, periphery of the stud comprises longitudinally-extending serrations.

5. A circuit breaker as claimed in claim 1, in which the press-fit means includes a stud fixed to the bimetal blade of the bimetal blade unit extending approximately at right angles thereto, said mounting unit including means defining a bore in which said stud may be relative- 1y non-rotatably slidably mounted and frictionally held, whereby the bimetal blade may be readily and relatively non-rotatably positioned in an infinite number of positions with respect to the mounting by pressing the stud into the bore to the required extent.

6. A circuit breaker comprising a mounting unit having a fixed contact terminal, a bimetal blade unit including a snap-acting bimetallic blade having highand lowexpanding sides, said blade comprising a substantially circular-shaped sheet bimetallic body having a substantially symmetrical centrally-located integral tongue connected at one end to the body of the blade and separated therefrom by a U-shaped slit, a press-fit connecting means including elements carried by and independently fixed to each of the mounting units and the tongue of the bimetal blade respectively for holding said units together in rigid, infinitely adjustable, relatively nonrotatably disposed operative relationship, and a contact fixed to the high-expanding side of the body of the bimetal blade adjacent the free end of the tongue and engaging the fixed contact of the mounting unit, said press-fit connecting means thereby facilitating the infinitely adjustable setting of the bimetal blade with respect to the mounting unit without relative misalignment of said contacts.

7. A circuit breaker as claimed in claim 6, in which the press-fit connecting means includes a stud fixed to the tongue of the bimetal blade extending approximately at right angles thereto, said mounting unit including means defining a bore in which said stud is slidably and frictionally held, whereby the bimetal blade may be readily positioned in an infinite number of spaced, axially aligned positions with respect to the mounting by pressing the stud into the bore to the required extent.

8. A circuit breaker as claimed in claim 7, in which the stud is provided with knurling on its periphery for frictionally engaging the inner periphery of the bore in the mounting unit.

9. A circuit breaker as claimed in claim 6, in which the body of the bimetallic blade has a spherically-shaped concavity on its high-expanding side symmetrically arranged with respect to its peripheral edge, the tongue of the bimetal blade being straight and fiat, whereby said tongue when heated moves the portion of the body of the blade to which it is attached to apply increasing pressure on the fixed contact of the mounting unit.

References Cited in the file of this patent UNITED STATES PATENTS 

